1. Field of the Invention
The present invention relates to a fuel injection control apparatus, and more particularly to a fuel injection control apparatus for determining a basic injection quantity of fuel according to a process which is different depending on the extent of a load.
2. Description of Background Art
Heretofore, processes for measuring an amount of intake air relative to a basic injection quantity of fuel have been known. The known processes include a direct process of directly measuring an amount of intake air using an air flow meter, and an indirect process of indirectly measuring an amount of intake air using a throttle sensor or an intake pipe negative pressure sensor. For example, Japanese Patent Laid-open No. Hei 4-365943 discloses a fuel injection control apparatus for calculating an amount of intake air from a throttle opening and an engine rotational speed in a transient mode of operation and detecting an amount of intake air using an air flow meter in a normal mode of operation. Japanese Patent Publication No. Hei 6-10437 discloses an apparatus for measuring an amount of intake air selectively according to a direct process or an indirect process, and correcting a calculated basic fuel injection quantity upon switching between the processes.
For a fuel injection control for motorcycle engines, the indirect process of the above two processes is often employed. When the load is low, a basic injection quantity is calculated from the detected value from the intake pipe negative pressure sensor and the engine rotational speed, and when the load is high, a basic injection quantity is calculated from the detected value from the throttle sensor and the engine rotational speed. Whether the load is high or low is determined from the throttle opening per engine rotational speed.
With regard to a motorcycle, the drivability at the time the throttle valve is slightly opened from a fully closed position, i.e., the response to an action to open the throttle valve, plays an important role in the overall driving performance and the commercial value of the motorcycle. The intake pipe negative pressure sensor has a poor output response to a change in the negative pressure. Therefore, when the motorcycle is in a transient mode of operation, a fuel injection quantity calculated from the negative pressure and the engine rotational speed is not accurate enough, resulting in a failure to provide good drivability.
The present invention has been made to solve the above objects. It is an object of the present invention to provide a fuel injection control apparatus for an internal combustion engine which is capable of increasing the drivability by improving the ability of changes in a fuel injection quantity to follow a throttle action.
To achieve the above object, there is provided in accordance with a first feature of the present invention a fuel injection control apparatus having a throttle sensor and an intake passage negative pressure sensor, for calculating a basic injection quantity of fuel from a throttle opening or a negative pressure detected by the sensor and an engine rotational speed, characterized by including first calculating means for calculating a basic injection quantity using the throttle opening and the engine rotational speed, second calculating means for calculating a basic injection quantity using the negative pressure and the engine rotational speed, means for comparing a rate of increase of the throttle opening with a reference value, means for detecting a load, selecting means for selecting said first calculating means when the load is high and selecting said second calculating means when the load is low, and switching means for setting said selecting means to select said first calculating means regardless of the selection made by said selecting means if the load is low and the rate of increase of the throttle opening is greater than said reference value.
According to the first feature, if the rate of increase of the throttle opening is large even if the load is judged as being low, the first calculating means is selected, and a basic injection quantity of fuel is calculated from the throttle opening and the engine rotational speed. Therefore, good drivability can be realized regardless of the output response delay of the intake passage negative pressure sensor.
According to a second feature of the present invention, the fuel injection control apparatus is characterized by further including full closure detecting means for detecting when a throttle value is substantially fully closed, wherein if said full closure detecting means detects when the throttle value is substantially fully closed when said switching means sets said selecting means to select said first calculating means, said second calculating means is selected. According to the second feature, when an abrupt deceleration is made to substantially fully close the throttle valve, a resetting process is carried out to select the second calculating means to use the intake pipe negative pressure in order to allow the fuel injection quantity to be controlled depending on the abrupt deceleration.
According to a third feature of the present invention, the fuel injection control apparatus is characterized by further including returning means for switching to said second calculating means when said negative pressure is substantially in agreement with a reference negative pressure set depending on the throttle opening if the load is low and the rate of increase of the throttle opening is greater than said reference value, thereby selecting said first calculating means. According to the third feature, the second calculating means is selected when the intake pipe negative pressure detected by the negative pressure sensor is brought into substantial agreement with the preset reference negative pressure, following the throttle opening.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.